Motor analyzer



June 10, 1952 D. J. WARD 2,600,088

l MOTOR ANALYZER Filed Nov. '13, 1945 4 Sheets-Sheet l 24 E J s W s n4 "7' 7/ Z7 251' a4 \9 2 l zu 55 a 62. 58 l 56 zz 5\ 7| H M 3!- Tz l u a 35 loa l m l 36 N9 P6. A 1, 14 G W9 PZ u C Kl 52 l l 60 v 24 i'. l 5 Bl L 26 N?.

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D. J. WARD MOTOR ANALYZER June 10,1952

4 Sheets-Sheet 2 Filed Nov. l5, 1945 D. J. WARD MOTOR ANALYZER June l0, 1952 4 'Sheets-Sheet 5 Filed Nov. 13,` 1945 s EN NU D. J. WARD 'MOTOR ANALYZER June `10, 1952 4 Sheets-Sheet 4 Filed Nov. 13, 1945 D.C VoLTAeE Patented `une 10, 1952 f oflone portion' withaanother fsimilariportiorr;

simple rlneansffrindieating 'whether one'fimped' ance is'greater=orlessethananotherz A? frtherlobjectlisithe Aprovision lofi-.means forindi'catiatthespercentageavariation:between'two A still'liurtheriobjeetis to .makeiitffpossihleitof read these variations: onta suitabiycalibrated scale.

Anotheriobjectf-ormy invention istoiprovide an electronic polarize'cFy alternatingzi current: galv vanometer.r i

Ineconnectionwith:.theilastr mentioned object,` it' '.isf; aifurther a object? tolm'ake the." responses of"- sucha: a'. gals'lanometer independent;y off. the" fre'F quencyioffthe current.'

It: isxa :still furthera object to'` provide. means: wheneloyequai f increments-#near "the" zero S centergaivanometer scalje will-"indicate `:relatively'fsmafll current fvariations' f and .equal l increments more# remote from th'e zero'i center will"indicate-relai" tivelydargecurrentvariatins:

Another object.issthexprovison in* an electronicv device r ofi afbridgev for "measuring purposes in' whichtheiarmscare impedancesiand/orfcapaci@ nfthosei-cas sizedfarmannee.,A

@nen of thepobiectsmfffthef. presentinve-ntion==is f theI-:provisionnotavfjig-.ffor;armature .testingeini whichthe necessary contactsffare automaticallyf madei f- Affurthenobiectfisetn m'akefthefJiereasiilvfad-A justabIeJor-larmatures that vary vin totalfiength 1 and; diameter land` in Whichthe commutatorsmayf also be of varying length and diameter.

In additionto making fprovisionsffor thegmore cammen motor \tests,.it is a further-object oiuny,Y invention to provide means v-vvherehy freversalsg; transpesitions,A and ishorted 'turl-is-i'xiayV ybe readily-f detectedfand located.

plane withlrespectrtcat leastrie on brushes-.c l A further object-:i orf` my.: inventienf-iss; thea pr visionfoffasuperior'systemfforfeifeetin than, wavefretincation 'altern mi@ liveriine-astoredfenergvfipfth samedetiolr S the rectilied current-during? thier inaetives i, cycle; Another obiectiie to maker-fiifpessle armatureftestingf;device-tarea 1v-adn@ or minst-thebrushes-for commuiamrswfaHymumr# ber'oftseementsg; Anoiherfobiect-fofemy;inventienfieftefm-akefiff.; possiblednfaidevicefOietheffr acier-wiesen, .f towreadilyftest andmeasure he insula ,n-bef. tween coilsf-f-find-` the farmaturezorfOtherfname 'tmf` WhchYthey-,arefwound-f-i A-vf urther; o bjeotfoff inventicneisetc vide a brush for certain purposes hereinate ex; p1aned-ffthats-vvi11gnotfsimultaneousiyemaleectact-w-ith-tvv'o @adjoining1isegnentsiandf'lthusisrt?. thefcoil toev/nich fsuch'rsegretsrarezfcenhetedi For:reasonsuhereinaftngfveshthfnenrsnrti ing brush construction, mentioned infthafstp'xe#r ceding paragraph.;:cannctlbemsdfioetne anis/ns that fee@ tneepvverlto thearrfzat fi tannini-'Mw dev-mea The con's'eciiietl showing-Muela;- cou- -bfi either-'fof the powerbr'shesidis rb tive? ba-iancefbtwe-eftnemoi 0fthefcentrarorfbaiaiice aeoobee Fig. 3 is a side elevation of the jig as shown in Fig. 2.

Fig. 4 is a detailed isometric drawing of two of the brushes used in the jig, and of their supporting means.

Fig. 5 is a cross-section taken on line 5--5 of Fig. 1.

Fig. 6 is a plan view that shows the mounting of one of the mandrels that hold the armatures in the jig.

Fig. 7 is a circuit diagram of the instrumentation network.

Fig. 8 is a diagram of a commutator oriented differently with respect to the brushes of my device than in Fig. 7.

Fig. 9 shows a modication of a portion of the circuits shown in Fig. 7.

Fig. 10 is a diagram of an alternative circuit that may be used with my jig, or for other impedance comparisons.

Fig. 11 shows another alternative circuit.

It has long been common practice to test one or more armature or iield coils by placing their terminals, or the commutator segments to which they are attached, across a source of electrical power. Such a test readily indicates an open circuit or a serious short Similar tests have been used to locate a grounded coil by manually making appropriate electrical connections to the armature frame and to one commutator segment. Such tests merely indicate whether the circuit is complete. By carrying similar tests a step further, the resistance of the circuit can be measured, and any unusual decrease of resistance may indicate, say, a shorted coil, and any abnormal increase of resistance may indicate that too much wire is somehow distributed in the circuit. Such a test, however, could not possibly indicate the nature oi the winding error.

The present invention goes much further than any such method of testing, and is based upon comparing the impedance of one or more coils with that of another coil or coils.

Inasmuch as the awkwardness of holding the armature has contributed to the difficulty and time-comsuming nature of armature coil tests, my invention comprises a special jig suitable for holding all armatures within a wide range of sizes. This jig includes means for making all the necessary contacts with the commutator and provides also for various other conveniences that will be discussed in detail as the structure is described.

The jig comprises four main parts: a housing A that supports and encompasses the various brushes, two relatively movable members Bl and B2 that carry mandrels Kl and K2 respectively, and a base D.

In the embodiment that I prefer, the housing comprises a side member E of circular shape at the top and partially supported by an integral depending portion F attached tothe base D. Member E has a central hole to permit one end of an armature to pass therethrough when the armature shaft is pivoted on mandrels KI and K2. A back wall G extends straight up from the rear of the base as far as the circular portion of member E, and its upper part is curved to form a partial cylinder having substantially the same radius as the circular portion of the end member E. The back wall Gr is transverse to member E, and one edge of the curvedportion is attached to the periphery of the circular part of the end piece E. A closure H, having the same radius of curvature as the curved portion of the back wall G, is attached to the upper end of the back wall by hinge J. The free end of the closure is straighted to conform to the outlines of the lower portion F, of member E, and it carries an operating knob i8 having internal threads in screw-threaded engagement with the reduced threaded end of a shank L which is integral with ball 19. When the closure member is in the closed position, the ball 19 is yieldingly held by the resilient detent H14, attached at its center back-portion to the base D.

The mandrel-carrying member Bl is mounted on a carriage Nl, which carries two L-shaped pieces a and b that extend around and under the base to serve as Ways when the carriage is moved longitudinally of the base. The mandrelcarrying member B2 is similarly mounted on a carriage N2 having two similar L-shaped ways, the forward one of which b may be seen in Fig. 1. Mandrel KI, adapted to hold one end of a motor armature that is furthest from the commutator, is pressed on otherwise rmly attached to the mandrel-carrying member BI. Mandrel K2 has a reduced shank e that is slidably mounted in the mandrel-support B2. Between the support B2 and the shoulder d, Fig. 6, the shank e of mandrel K2 is surrounded by a compression spring to urge this mandrel toward the other. A pin Q extends through the shank e on the side of support B2 opposite from spring 8U. An operating handle W, curved substantially as shown, is slotted intermediate its ends to straddle the portion of shank e that lies between pin Q and the mandrel support B2. The lower end of handle W is pivoted on post T, rigidly attached to support B2.

A centrally apertured disc 58, formed of insulating material, is mounted on the inside of end wall E. Two concentric insulating rings 22 and 23 are attached to discs E and 58 by means of screws 2t, the heads of which overhang the respective strips in which they are placed. These arcuate strips and screw heads together form ways for slidably mounting two arcuate insulating supports 25 and 26 on opposite sides of the center holes in discs E and 58. Two posts, 21 and 28, are rotatably mounted on arcuate supports 25 and 23 respectively. One end of a bar 29 is rigidly attached to post 21, and another bar 30 is similarly anchored to post 28. Blocks 3l and 32, disposed intermediate the ends of bars 29 and 3U respectively, are integral with these bars. The tapered brush 34 has two holes therein, one of which is threaded. The untapped hole is adapted to receive the free end of bar 29. An adjusting screw 36 is threaded through the other hole in brush 34 and then through a clearance hole in block 3|. The end of screw 36 passes through a hole in post 21 that is large enough to clear the threads of the adjusting screw. Nuts 3'1 and 38, soldered or Welded to screw 36, are disposed on opposite sides of post 2'! so that the screw is restrained against longitudinal movement while turning. Brush 35 is mounted in the same manner as brush 34. and has an adjusting screw 39 in threaded engagement with the brush, the end of screw 39 being rotatably supported in post 28. Block 32 has a clearance hole therein to assist in holding the screw in place.

A third post 40 is mounted directly on the insulating disc 58. On this post is pivoted an arm 4l (shown in some detail in Fig. 4) made of Bakelite or other appropriate insulating material. Brush 42 is directly mounted on the end f arm" 41 by means of screws'4t` Brush '4l' is composed of a `conducting half I3 and `a nonconducting half M, bothterminating in a single knife edge "45 to vprevent the `sfhorting of adjoining c'cm'mutator bars. Another identical brush 41 is attached 'to a spring 'member 4 8, the conducting naif '49 being soldered ler welded to Ithe spring member 'andv the non-conducting half 5i! rbeing screwed to the 'conducting 0l' metal Dertien '4'9. The opposite end fof spring 48 fis attachedto 'the noncoiductirig arm 4l by means jef screws 52 and 5t.l Between these screws landbr-iisl'i 47. v'the spring is provided with a bend or loop substantially as Vslil'oi'i'r'i'l in Fie. 4. A block 55, attached by screws 55, extends transversely across arn 4l between the loop 56 and ithe brushes, the 'portlbi abo've th'e 'spring f48- being cut -awa'y 'to iperifllt the fie end` of 'the S'ifigto-fx as well fas te "incre :longitudinally fas far back a's the f-loc'p. vscrew -51 is threaded th'rollgl'l block 5'4 sothat the end opposite the screw head bears against lthe spring. fflle tendency of loop 56 to fex'p'and causes brush El 'to move :outwardly whenever Vscrew 51 is loosened, but when Sit .is trnedso that it moves longitudinally toward the le'o'p,vthe bril'sh is caused to fm'ove back. `Screw 51 thus permits brush 47 vto be moved 'relative to bru`s}h '42.

fspri'ng's e9, 6e 'and 6l, 'attached to yarms 229, 3e and Il respectively, are appropriately anchored atI ftlieirother 'ends "to 'the Ynon-conducting memb'eisi25, '2u-"and '58 respectively. These springs Seite to yieldi-Ilgly hold the 'brushe'sn contact withth'e commutator of the armature when it is pivoted between mandrels PI and P2.

Y-Pis'tsli'rh 63 and {i4-are mounted onthe rotatable noli-'conducting members 25, 26 and '58 respectiyely. These springs serve to Ayieldingly hold the `brushes Vin contact with the 'c'ommutator of the Vvarmature when lit is pivoted between mandrels Pl fand P2.

vo's'ts 52, 63 and v(ill, lmounted on the rotat'able non-'conducting disc2l, serve to engage arms 29, 3`0 n*and 540 Vresrie'ctively 'and l-move the brushes away from 'the 'commutator as fthe closure AI-I is raised. This V-is effected through clockwise rotation f'ffdis'c k2l `to which oneendof link 566 -is pvt'ed, the other `end -of lthis link *being "pivoted -to'iura'cket-s's attached to the closure H. whenever 'the lid is raised, the brushes are thus k'out f sthe"way, permitting armatures to `vbe 'placed in the "jig iand removed without interference.

.'narinatureis placed in the jig inthe following manner. First, Y the operator vmust make s''r'e that `the man'drelecarrying supports `IBI and l"32 are .positioned 'so' rthat the commutator 'is disposed in proper relationship to ythe brushes andso that the distance between the ends of the l'a'll'el's 4Kl and K2 is slightly less 'than the length'of the armature shaft. If vthe `mandrels 'are not already suitably positioned, they may be iiiove'd and re-positioned. This is 'done by re'- ea'silg stfsclews Vwhich :"n'or'hially "bear upon the biase-D'and tighten the `four Ab-shaped members a'ins't'the lwere'dge i of the'base .When these sc'fews are -`1o`0`S'lfled, the carriages Nl and N2 ly bhlovedleng'thwise of thelase, thuspel'rvmitting the Yirland'rels to be re-'positioned and 'spaced "according to the Y:requirements "just men- -tio'ned. The tightening 'of `the set-screws in carriages NI and N2 'will anchor the `carriages in the new positions to which they have been adjusted. It 'will Vbe assumed l*for the Apresent =that the "coils 'Pl 'and "152 'and their *associated with the circuit`s) areliar enough back to be-fout of the way for the armature that is to beplaced in the jig. While the closure I-I is in lits raised position, the handle W is. moved to the right, causing it to bear upon pin Q, thus moving mandrel K2 to the right against theac'tion of spring 80. The armature may then beplac'ed between 'the ma'ndrels with the centers of the two-'ends of the armature shaft in vengafgem'ent with the mandrel points. Uponreleasixig handle W, spring `t!) will urge mandrel K2 Ytowardf-tlzfe leT't, thus holding the shaft in 'proper aligzmrent between the two 'mandrels When 'the closure .is lowered, disc -2l .turns countersclockwise, permitting 'the brushes 'fito move inwardly until they Vcome into l'contact' with the commutator yof 'the armature.

A switch 61, attached to base D, opens and closes one of vthe circuits (later ato be described) that indirectly supplies power to .the brushes. inasmuch as this `switch is vnormally open, the current is always olf when the yclosure raised. When the 'closure vis lowered, it lengages operating member 68 'of switch v(il, thus fenergizin'g the brushes. =In the lclosed position, the l-id I-I protects the :operator .from the high vvoltages, `but he nevertheless has easy access to-:the end of thearmature .nearest to postB'l., to which is attached a support 'll on which :he may irest his vleft hand whileslowly turning the armature in order properly to conduct the tests laterfto be fdescribed and heimay watch what he is doing through the window'fBQ in the closure.

Knob 1l, carrying lan indicator 1.3, is :keyedto shaft 1-2, 'on the other end of 'which is mountedl a disc, or double eccentric, 14. Two links, 1'5 and 16, are pivoted to thisdisc at .points displaced from the center, andthe opposite ends rof these llinks .are pivoted respectively to the arcuate members 25 and 25. .It will bejobserved'thatthis mechanism, upon rotation of knob 1I, moves brushes 34 and 35 bothcloser to, or further from, the brushes carried by arm 40. This adjusts the fbrushes 35 and 65 so that they will be properly positioned for the number of segments in the commutator of the particular larmature under test, Aas `indicated on scale 'I1 with which the .pointer 13 cooperates. The nature of :the adjustment'thus made lwill be more fully vdiscussed in connection with the circuits.

The jig is connected to an instrumentation network, one form 'ofwhich is illustrated in Fig. 7. I obtain the voltages to operate the system fromva 4000 cycle oscillator and power amplier having i a 'conventional power supply. This alternating current source -83 is indicated in the left portion of the ligure. Conductors 8| 'and-'82 are connected to this current source. Resistors R2. R3 and :R4 are connected in `series a'crossrthese conductors in the manner shown, R3 "being fa Variable :resistor or 4'potentiometer havinga slider 84 `whichmay'be 'adjusted forzero potentialiin a manner later vt0 be described. 'These Ythree re= 'sistorsform onefarin of an alternating current bridge. The .three ,'pole, double-throw switch S2 -is "used for connectingvint'o the circuit v.the ini-e pedances'that are to form *the second 'arm'of the bridge. Blades 85 and 88 are respectivelyconnectedtoconductors il! and-2 by'wires85-:a'nd'81 respectively. When Vthese blades Aare lon the upper fc'ontacts '89 and 96, `connection fis :made :by wires 192fand -93 to the'power brushes 34and1135, "shown at the right .in the electrical idiagramfand previously-referred to inconnec'tion withLthejig'.

structure 'flater to 'be described Vin 'connection 75 Tneseabrushesb'ear thefs'amereference'inumersls 7 V as in Fig. 1. The coils on the two sides of the armature 9| (that is, on opposite sides of the power brushes) are in parallel. Otherwise stated, inductance ZI and Z2 are in parallel with inductance Z4. These impedances, connected across conductors 8| and 82 by switch S2', form the second arm of the bridge.

When the three-pole double-throw switch S2 is in the position described, blade 94 will be on pole 95, thus connecting brush 41 and wire 9E to conductor 91. When switch S| is closed, the balance arm of the bridge then consists of brush 41, conductor 99, blade 94, conductor 91, switch SI, conductor 99, the primary of transformer Tl, and conductors |99, IUI and |02, the latter connecting to the wiper 94 of the variable resistor R3. When the impedances ZI and Z2 are equal respectively to the impedance offered by the resistances in the rst arm on opposite sides of the wiper 84, there will of course be no current in the balance arm of the bridge and transformer TI will not be energized. If the impedances in the second arm of the bridge do not balance the corresponding impedances in the rst arm, current will flow in one direction or other through the balance arm. The resulting current in the primary of transformer TI will produce a voltage in the secondary. thus placing opposite potentials on the grids of triodes VI and V2. These two triodes rectify the current in two circuits connected in parallel across the main conductors 8| and 82. The first circuit includes the triode VI, a filter which comprises choke T3 and condenser C3, and the resistors R1 and RB; and the second circuit includes triode V2, the filter consisting of choke T4 and condenser C4, and the resistors RI 0 and RI I. These circuits might be considered the first and second arms of a second bridge.

Because of the high inductance of the chokes T3 and T4, very little current flows through them. I therefore connect diode V4 from conductor 82 to a point between choke T3 and triode VI, these valves being arranged so that their directions of conductivity are opposed. As a result, the energy stored in choke T3 passes through diode V4 during the half-cycle when triode VI is non-conductive. This current reaches point |63 through resistor R8. In the second arm of the second bridge, diode V6 is connected across choke T4 and condenser C4, the connection on one side being made direct to the main conductor 82. This diode is conductive on the half cycle when triode V2 is non-conductive, and, like diode V4, it permits the energy in its associated choke to be discharged around the choke and through resistor RII and part of resistor RI to slider |23. Diodes, rather than condensers, are employed to bypass these chokes, because we are dealing with an integration of the entire half cycle wave instead of merely with the peak, as would be the case if condensers were used instead of valves.

Resistor R9, the Zero-center D. C. galvanometer M, and resistor RIZ form the balance arm of this second bridge, and slider |23 is adjusted so that there is no current in either direction through the meter when transformer TI is not energizedthat is, when there is no current through the balance arm of the first bridge. Resistor R|2 is variable to provide a compensation adjustment for the A. C. voltage applied to the network, and permits the meter M to function properly irrespective of the applied voltage. Resistor RIZ is shunted by condenser |24 to eliminate spurious A. C. pickup in the wiring of the various components, The use of diodes V4 and V6, rather than condensers, enables the galvanometer M to respond to a condition more nearly approaching the average voltage of the half cycle than would be the case if condensers were employed.

The remainder of the network will be better understood if we rst explain the functioning of the circuits and components already mentioned. Let us suppose that we throw the three-pole, double-throw switch so that blades 86, 94 and 88 respectively engage contacts |25, |25 and |21, and that these contacts have been connected to impedances ZI' and Z2 whose values are to be compared. These impedances now form the second arm of the rst bridge previously described, and the balance arm consists of conductor |28. contact |26, blade 94, conductors 91 and 9B, switch Sl, conductor 99, the primary of transformer TI, and conductors |09, IOI and |02. If the voltage drop across each of the impedances ZI' and Z2 is equal respectively to the voltage drop across resistors R2 and R4, there will of course be no current through transformer TI and the grids of the triodes VI and V2 will have the same potential; but if impedances Z I and Z2 are not of equal value, the phase of the current flowing through the primary of transformer TI will depend upon which impedance is the greater. The grids of the triodes will thus have opposite potentials whose difference will vary with the extent of variation in the values of the impedances ZI' and Z2'. This will result in the presence of unequal D. C. voltages on condensers C3 and Cri and at point |93 and wiper |23, the relative polarity of which will be indicated on meter M in the balance arm of the second bridge.

If either impedance ZI or Z2 is very much greater than the other, or if a short occurs across one of the two elements in this second arm of the first bridge, the resulting difference of potential on the grids of the triodes might be great enough to produce a sufliciently excessive current through the meter M to injure the meter movement. Biased diodes V5 and V1, connected in reverse parallel across the meter and resistor 9, provide a means for preventing such injury and also afford a means whereby a given angular movement of the galvanometer needle near the aero center of the galvanometer scale will represent a smaller current variation than the same angular movement near the outer ends of the scale. Diodes V5 and V1 are biased respectively by batteries |29 and |30, either or both of which could equally well be placed on the opposite side of the associated diode. When the IR drop through the resistor R9 and the meter M exceeds the algebraic sum of the bias voltage and the cathode emission voltage of the diode V5 or V1, whichever is of correct polarity, a portion of the current iiowing through resistor RI2 is bypassed around the meter, thereby changing its sensitivity as an indicator of the total current flowing through this resistor. The bias voltages may be adjusted so that the sensitivity changes at any desired point. In the iirst model built, this was adjusted so that 50% of the scale on either side of zero represented a 15% unbalance in the impedances under test, while the remaining of a unbalance was represented by the remainder of the two sides of the scale. The biased diodes thus conduct a small amount of a weak current but carry the greater portion of a strong current.

Diodes V4 and V1 are encased in the same envelope and diodes V5 and V6 in another. The reason for this will be apparent if we examine sacoches lf Whenthe switch S3 is in its fourth position from the left, resistor Rlo will be alone on one kside of the balance arm, and theimpedance of resistor .R11 will be added to the otheri side. The value of resistor R11 is such that this shift creates a unbalance in one direction, thus enabling the operator to check the calibration of the dial of galvanometer M. When switch S4 is in its fifth position from the left, which is also the extreme position to the right, RIS will be alone on one side of the balance arm and the impedance of resistorRl will be added to the side opposite that on which it normally belongs. This creates a 10% unbalance in the direction opposite from that created when the switch is in its fourth position, and the calibration of the galvanometer dial may thus be checked on the side opposite the one previously checked.

As set forth in the objects, the jig and instrumentation network herein described may be used for a variety of tests. Let us consider how various armature faults are indicated by portions of the jig and instrumentation network that have already been described.

The armature is placed in the jig in the manner previously described, and the lowering of the closure H causes the brushes to make contact with 4the commutator and closes the switch E1, causing the power brushes to receive their respective potentials. If dial 1l has been properly adjusted to bring the indicator 13 into alignment with the number on the scale 11 that corresponds to the number of segments on the commutator, there will be the same number of commutator gaps in the quadrant between the power brush 35 and the two brushes 42 and 41 that there are in the quadrant between the power brush 34 and the brushes 42 and 41. These quadrants will hereinafter be referred to as the first and second quadrants respectively. If the number of commutator segments is a multiple of four, the adjustment of dial 1l will dispose the power brushes diametrically opposite each other, both equally distant from a line midway between the brushes 42 and 41. This condition is illustrated in Fig. l. When the number of commutator segments is not a multiple of four, it will readily be understood that the power brushes cannot be disposed exactly 180 degrees apart and still keep the same number of commutator gaps in the first and second quadrants in order that the same number of coils might be in circuit to form the two elements of the bridge arm. The power brushes must therefore both be moved closer to or further from the center brushes 42 and 41; but whatever the num- Vhis right hand free to operate the various controls), the impedances Z2 and Zi, Fig. '1, corresponding to the coils in the first and second quadrants respectively, are substantially equal. If the galvanometer shows a material deiiection in either direction, the trouble may be an open, shorted or reversed coil, a transposed connection, an exces- Cii sive winding error, a non-symmetrical commutator or defective insulation.

An open coil will cause the balance indicator M to deiiect to the right-hand side during the time the open coil remains in the rst quadrant unless the open wire is arcing over, in which case the location will be self-evident. When the open coil moves to the second quadrant, the galvanometer will immediately shift to a 100% lefthand deflection. Consequently, the exact coil which has the open circuit can be located by 0bserving which commutator bar passes the balance brush when the defiection reverses its direction.

Inasmuch as the device is powered by highfrequency A. C., a shorted turn will act as a transformer with a short-circuited secondary which reects a low impedance into the primary. In the analysis, this impedance will generally represent an unbalance of between 50% and 100%,and the indicator will deflect to the left when the short is in the rst quadrant and shift to the right when the short transfers to the second quadrant. The exact coil having the error is thereby located.

The impedance eiect of one reversed coil in an armature is the equivalent of the omission of two coils, inasmuch as the flux of the reversed coil cancels the flux of an adjacent coil. Consequently, if the operator were testing a 32-coil armature which had one coil reversed, the impedance of the quadrant in which it happened to be positioned would be the impedance of only 6 coils, whereas the impedance of the other quadrant would be that of 8 coils. It may be noted that almost all reverses of a single coil will reflect an unbalance somewhere between approximately 20% and 50%. The reversed coil may be located as it moves from one quadrant to the other.

If two pairs of wires in a continuously wound armature have been reversed, one coil will be added or subtracted from the first quadrant as one of the commutator bars connected to the transposed Wires contacts brush 35, and as the second bar connected to the transposed wires contacts this brush, the opposite condition is indicated. After the two segments have cleared brush 35, no further effect will be noticed until the same bars cross the balance brush 41. The effect then will be that of first adding one coil to one quadrant and subtracting it from the other, and then to reverse this condition with the next commutator bar. After the two segments have cleared the balance brush, no unbalance will again be noted until the two segments cause the same deflection first in one direction and then in the other as they pass under brush 34 and leave the second quadrant. It will thus be noted that for each revolution of the armature, three positions will be found at which the balance indicator deiiects rst in one direction and then in the other. All three of these will take place in the first and second quadrants, and none will occur elsewhere.

To determine errors in the number of turns wound into the coils of the armature, the instrument is especially provided with high sensitivity in the region immediately adjacent to, and on both sides of, the center zero. It is possible to read an impedance unbalance of one-half of one per cent. However, it is not normally deemed necessary to reject coils for less than 4 to 10% unbalance.

If the commutator on the armature is nonf symmetrical to the extent that the distance be- 13 tween one of the power brushes and the ybalance brush varies more than the distance between the balance brush and the commutation suppression brush, there will be a deection of the galvancmeter at each point of commutation of a power brush from one segment to the next. However, this dancing deflection will continue to be in one direction as the armature is yrotated from bar to bar,- then the deflection will cease for about one quarter of a revolution and will begin again in the opposite direction. There will be no immediate change in the direction of deflection as a single commutator bar passes from one quadrant to the other. The distance between the balance brush 41 and the commutation suppression brush 42 may be adjusted to make the instrument give these indications of non-symmetry for any amount below one-half the width of a commutator bar.

The portion of the network in the upper left hand corner of Fig. 7, affords the means .for a very sensitive insulation test. When switch S2 is turned so that the center blade S4 is on 'contact 95, the grid of triode V12 is connected to the balance brush il through wires 131 and 91, blade 94, contact 95 and wire 96. The armature shaft or frame is grounded -by means of the jig, as indicated in Fig. 7, and it will be noted that the negative side of the D. C. voltage supply is also grounded. Resistors R14 and R15 are connected in series across the D. C. voltage supply wires, and the meter M2 and resistor R13 are connected in series between the cathode of tube V12 and a pointl between resistors RM and R15. When there is an innite insulation resistance between the frame fof the armature and the coils or commutator segments, the grid potential will be due solely to the voltage drop across resistor R I. There will thus be a low voltage drop through the tube and a proportionately high voltage drop through resistor R13 and the meter, which con sequently gives a full-scale deflection. If there is a finite insulation resistance to ground, the positive potential on the grid of tube V12 will drop, thereby increasing the resistance through the tube and decreasing the meter deection. When such an indication occurs, the exact location of the insulation break-down can be determined by opening switch S1, thus making connection through the ground and condenser Cl to the balance arm of the A. C. bridge. The deection of the galvanometer M1 will be to the left if the grounded coil or segment is in the first quadrant, and to the right if it is in the second quadrant. The direction of deflection will change as the grounded coil or segment passes from one quadrant to the other.

When stators, elds or other such impedances are to be tested, the coils may be compared by connecting one lead from one coil to contact 125 of switch S2, connecting one lead from the-other coil to contact 121 of this switch, connecting the other leads of the two coils both to contact 128, and throwing the switch so thatthese contacts are in circuit. Shorts, open circuits and winding errors are then indicated by the galvanometer in the same manner as for armature coils.

Ii the coils are connected in the fashion just described, the meters M and M2 will give the usual insulation and ground indications when the pairs under test Aare placed upon a grounded metal plate so that their frames or cores make contact with the metal.

The coils Pl and P2, Fig. 7, which locate the neutral plane of an armature, are disposed on '14 opposite sides of the power'brush 35 vand may be adjusted 4by means-of thev structure shown in Figs. l, 2, 3 andv 5, so that the pointsof their cores105 and 106 come into -lclose proximity with the armature core. Inasmuch as suchV armature cores are of various diameters and vary in their distances from the commutator, provisions must be made for adjusting coils P1 and R2 radially (that is, toward-or from the main axis of thejig) as well as longitudinally. Other purposes, later to be explained, require that they also be .angularly adjustable. The structure that makes the radial, longitudinal and angularadjustments'pose sible will now be explained. y

A short cylindricall vmember Ill-'1, rotatably mounted in the central holes in :members E and 58, has a .liange |08 attachedto the end inside the jig by screws 109. A relatively large at ringl1 l vis similarly aflxed toV the opposite end -of member I-l. A radial projection 11.11 integral with ring 110 ycarries an axially extending bar H2. A slotted member 113 isV transversely mounted on bar 112 in such a manner that it may be moved radially and xedin adjusted position by means of screwsV 114. Af-block'H-S is rigidly attachedtothe under side of the lower end of member 11.3. This block is slotted 'to receive an axially movable barV H 5, and a set screw Hl serves to hold bar 116 in adjusted position.

A bracket 11'8 is welded or votherwiserigidly .at-

tached to bar 16. This bracket 118 carries-the two coils P1 and P2 with their `pointed .pole :pieces lee and 1&5. These coils and pole pieces may be-moved axially along the armature -by Athe longitudinalzadjustment of member |16, and they vmay be adjusted toward or away vfrom thearmature by means ofbar 113' and the screws |14.

Inasmuchas the current inthe armaturclcoils on opposite sides of brush 35 dow` in Opposite directions, the magneti-crlux cutting -coilsP-I and P2 will also be in opposite directions Vand will therefore generate opposing currents in these coils. YIf theilux is egual through both coils, the opposing currents will neutralize each-other, With the result that lamp 1;!'9v will not light. When the coils are so adjusted'` with respect 'to the armature that the 'lampdoes not light; the neutral plane of the armature passes midway be tween the coils. If the armature has the proper symmetry and the coils are properly Wound. Athe neutral plane will pass through theV power brush 35. The location of the neutral plane' should therefore be determined with vrespect to this power brush, and either the calibrated scale .or

. the indicator must consequently'be located on,

or movable with, the varcuate segment en which the power brush is carried-that is, segment .26. In practice, I place vthe calibrated scale 12,0 .on this segment and make the pointer 121 integral with V:dange 10B. The scale isso calibrated that whenl points .195 and 106 are requally distant from power brush 35, `the pointer Will be on zero. If the lamp 1 1S lights when the pointer is so `positioned, the neutral plane Vis not in a Symmetrical position. The actual position of the neutral plane may then be vlocated by moving .handle E22, attached to member 111), either clockwise or counter-clockwise, until the lamp goes out. The pointer 121 will then indicate on scale |2the number of degrees that the neutral planchas shifted either to the right or left of its symmetrical position.

. An explanation of Fig. 9, which shows modi-V cations applicable to the network of Fig;- 'L requires that we `examine certain phasesgof the 15 operation of the said network. When the potentials on the grids of triodes VI and V2 (Fig. '7) are equal, due to an absence of current through transformer TI it will readily be understood that an increase of voltage across conductors 8| and 82 will result in an equal increase of current through the two triodes. In such a situation, the increase in supply voltage will therefore not unbalance the direct current bridge that includes the galvanometer M. But if there is an imbalance in the coils being tested, the resulting current through transformer T| will place unequal potentials on the grids of tubes V| and V2, and although these unequal grid potentials will of course not change in relative values when the supply voltage is increased, they will produce a greater variation in the current flowing through the two tubes at the increased voltage than at the lower. For a given percentage imbalance through the balance arm that includes the primary of transformer TI, there will thus be a greater current through the galvanometer M with a high supply voltage than with a low supply voltage. In the network as shown in Fig. '7, resistor RI 2 is made variable to compensate for the effects of such changes in the supply voltage. Fig. 9 shows an arrangement whereby these changes are automatically compensated for. This diagram shows the metering or balance arm of the second bridge-that is, the direct current bridge-and points |03 and slider |23 are those having the corresponding numbers in Fig. 7. In following the explanation of this circuit, it is to be remembered that all parts of the network may be identical to those shown in Fig. '1 excepting for the changes shown in Fig. 9. The primary of transformer T5 is connected across the conductors 8| and 82 carrying the A. C. voltage supply. An increase in this voltage increases the voltages in the secondaries of this transformer, producing a correspondingly increased negative potential on the grids of triodes V8 and V9. This in turn increases the resistance through these tubes to compensate for the increase in supply voltage. When the current in the balance arm between point |03 and slider |23 is in one direction, it is conducted through one of these tubes, and when it is in the opposite direction, it is conducted through the other. The four condensers shown assist in ltering.

Fig. l0 shows a modiiied network for accomplishing the same over-all polarized vindication achieved by the network of Fig. 7. In this system, the ground insulation is indicated directly on the ohmmeter M2a. The A. C. balance arm is substantially the same as in the circuit of Fig. 7, the primary of transformer TI being connected from the balance brush 42 to the A. C. midpoint 84, which is at the same potential as the cathode and plate respectively of the rectifying diodes Vla and V2a. When there is no imbalance current in the transformer TI, any current that may be flowing through diodes Vdc and V511. and their associated resistors will be equal; but when the primary of TI impresses an imbalance current on the secondary, then the potentials on the plates of valves Vdc, and V50. will change in accordance with the direction of the imbalance current, and the current through these valves will also change accordingly. The cathodes of these tubes will have potentials that vary according to the respective voltages applied to the plates of these tubes and the direction and amount of deiiection of the indicator of galvanometer Mla will correspond to the relative values of these potentials, thus giving an indication of the imbalance of the two impedances under test.

Fig. l1 shows another modified network em bodying my invention and achieving the same over-all result as the networks of Figs. '7 and 10. In this circuit, the primary of transformer Ti that carries the imbalance current is coupled inductively to two secondaries HH and |52, to which the grids of triodes V301r and Vdc are connected. When there is no current in either direction through the primary of transformer Tl, there is no difference of potential on these grids, but when transformer TI is energized by an imbalance current, the grid potentials change according to the direction and degree of imbalance. The re sulting change in resistance through tubes V3a and Vea changes the D. C. mid potential at point |63, and current ows through the galvanometer M b in accordance with the direction and strength of the imbalance current, thus giving a visual indication on the scale of the imbalance of the impedances under test.

My invention may be embodied in many other forms, the jig and networks shown being only representative embodiments. Various modifications, omissions, additions and transpositions may be made from the illustrative embodiments shown and described without departing from the broad spirit of my invention as set forth in the appended claims.

My claims are:

l. In a device for comparing impedances, a combination including: rst and second conductors connected to an alternating current source; impedances connected across said conductors for forming a first branch of a Wheatstone type bridge; means whereby two impedances that are to be compared may be connected in series so that the said two impedances form the two ratio arms of a second branch of said bridge; an electrical path from a point intermediate the said two impedances to a predetermined reference point in said first branch; and a polarized, alternating current galvanometer system comprising (a) iirst and second branches of a second Wheatstone type bridge connected across said conductors, each of said branches of said second bridge comprising a first arm including a triode and a filtering system and a second arm comprising a resistor, (b) a polarized direct current galvanometer having one side connected to a point between the arms of one branch of said second bridge and the conjugate point of the other branch of said second bridge, and (c) means responsive to avoltage imbalance across said electrical path for impressing opposite voltages upon the grids of said triodes to render the rst arms of the two branches of said second bridge unequally conductive, thereby causing the galvanometer to indicate the magnitude and direction of said voltage imbalance across said electrical path.

2. In 'a device for comparing impedances, a combination including: an alternating current source; impedances connected across said source to form a rst branch of a iirst Wheatstone type bridge; means whereby the two impedances that are to be compared may be connected in series across said source to form the ratio arms of a second branch of said first bridge; an electrical path from a point intermediate the said ratio `arms and a predetermined reference point in said first branch; a second Wheatstone type bridge each branch of which has a first arm comprising a triode and a ltering system and a second arm comprising a resistor, the balance arm of said second bridge comprising a polarized direct current galvanometer; two electronic rectiers connected across said galvanometer so that they are conductive in opposite directions; means for biasing said rectiiers so that equal increments near the zero center of the galvanometer scale represent small current variations and equal increments remote from said zero center represent relatively large current variations; and means responsive to a voltage imbalance across said electrical path for impressing opposite voltages upon the grids of said triodes to render the iirst arms of the two branches of said second bridge unequally conductive, thereby causing the galvanometento indicate the magnitude and direction of said voltage imbalance across said electrical path.

3. In a device for comparing impedances, a combination including: an alternating current source; impedances connected lacross said source to form a iirst branch of a Wheatstone type alternating current bridge; means whereby two impedances that are to be compared may be connected in series to form respectively the two ratio arms of the second branch of said alternating current bridge; an electrical path from a predetermined reference point in the first branch of said bridge and a point intermediate the said ratio arms; a Wheatstone type direct current bridge, each branch of said bridge having (1) a rst arm comprising (a) a triode and (b) a filtering system that includes an impedance and a diode, said diode so arranged with respect to said triode that the energy stored in the choke will pass through the diode during the half-cycle when the triode'is non-conductive, and (2) a second arm comprising a resistor; the balance arm of said direct current bridge comprising a polarized galvanometer; land means responsive to a voltage imbalance across said electrical path for impressing opposite voltages upon the grids of said triodes to render the first arms of the two branches of said direct current bridge unequally conductive, thereby causing the galvanometer to indicate the magnitude and direction of said voltage imbalance across said electrical path.

4. In a device for comparing impedances, a combination including: an alternating current source; a Wheatstone type alternating current bridge connected across said source; means whereby two impedances that are to be compared may be connected in series to form respectively the two ratio arms of one branch of said alternating current bridge; a transformer having its primary connected so as to form the balance arm of said alternating current bridge; a Wheatstonetype direct current bridge connected across said source, said direct-current bridge having a triode in corresponding arms of each of its branches; the balance arm of said direct current bridge comprising a polarized galvanometer; the secondary of said transformer connected to the grids of said triodes, said secondary acting in response to a voltage imbalance in said primary to impress opposite voltages upon the grids of said triodes to render said corresponding larms unequally conductive, thereby causing the galvanometer to indicate the magnitude and direction of the voltage imbalance in said primary.

DELBERT J. WARD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 879,061 Pierce Feb. 11, 1908 1,316,244 Kemble Sept. y16, 1919 1,358,179 Schweitzer Nov. 9, 1920 1,432,003 West Oct. 17, 1922 1,496,786 Shackelton June 10, 1924 1,825,514 Fitzgerald Sept. 29, 41931 2,006,806 Hagen July 2, 1935 2,135,587 Lovelady Nov. 8, 1938 2,360,618 Pash Oct. 17, 1944 2,394,892 Brown Feb. 12, 1946 OTHER REFERENCES General Electric Review, May 1941, pages 263- 266. 

